Spline connections are used to provide for the transfer of torque from one shaft to another. The splines have gear like teeth meshing the mating internal and external splines.
The loaded shafts twist experiencing angular displacement along the length. This occurs not only throughout the length of the shaft but also throughout the spline, with the twist of the shaft varying as the load is transferred to and from the particular shaft. Maldistribution of tooth load and stresses therefore occurs.
With straight teeth the load is predominantly at the end locations of the spline. High bearing stress and high tooth bending stresses are experienced. These high stresses reduce the low cycle fatigue life.
It is known to crown spline teeth with the crown located in the center, in order to achieve a more uniform load distribution.